Play notes being added to a chord.

When entering notes via midi, if the first note is held down while
more notes are played, to enter a chord of notes, only the first
note sounds. This patch allows the subsequent notes to be heard.

NB. If two notes are pressed at exactly the same time so that they
are both processed in a single call to Score::processMidiInput(),
then still only one of them will be heard.
fix #20174
Merge pull request #233 from lvinken/musicxml-fixes

fix #20174
Merge pull request #232 from softins/play-midi-added-notes

Play notes being added to a chord.
fix text palette handling
change edit mode implementation
updates for new element edit mode schema
strong typing of ArpeggioType
std::nan not available on mac
fix delete/add start/end repeat bars in scores with parts
fix #10054: Parts don't preserve stem direction